1. Field of the Invention
The present invention relates generally to a wireless communication system based on multiple carriers, and more particularly to an adaptive bit loading technique for optimizing the performance of a wireless communication system.
2. Description of the Related Art
Interest in a multicarrier modulation technique has recently increased as a result of an increased need for high-speed data transfer. An Orthogonal Frequency Division Multiplexing (OFDM) technique serving as the multicarrier modulation technique is different from a single carrier modulation technique that must use a complex adaptive equalizer. The multicarrier modulation technique divides data into sub-channels and transmits the sub-channels that independently have Additive White Gaussian Noise (AWGN), but do not have Inter Symbol Interference (ISI).
Although the multicarrier modulation technique does not require an expensive equalizer, it does require complex power control and complex power and bit loading in order to maximize system performance.
Various bit loading algorithms have been proposed which can maximize noise margin and optimize system performance while addressing the problems related to limited bit rate. However, it is difficult for these algorithms to be applied to real systems.
Because adaptive bit loading is very sensitive to time-variant characteristics of wireless transfer media in wireless OFDM systems, it requires a feedback mechanism for feeding back a Channel Quality Indicator (CQI) to a transmitting side.
In terms of a wireless system, an OFDM system using multiple transmit/receive antennas has been proposed to improve a data transmission rate. A multiple-input multiple-output (MIMO)-OFDM system has a very complex problem in bit loading. To address the problem in the bit loading, a greedy algorithm and other modified algorithms have been proposed as optimized algorithms. However, these algorithms require high computational complexity.
Accordingly, a need exists for an adaptive modulation technique that can be optimized in all systems while reducing implementation complexity.